Isocyanate percent

Hydroxyl Number. The molecular weight of polyether polyols for urethanes is usually expressed as its hydroxyl number or percent hydroxyl. When KOH (56,100 meg/mol) is the base, the hydroxyl number is defined as 56,100/equivalent weight (eq wt). Writing the equation as eq wt = 56,100/OH No. allows one to calculate the equivalents of polyol used in a urethane formulation, and then the amount of isocyanate required. The molecular weight can be calculated from these equations if the fiinctionahty, is known mol wt = / eq wt. 

At failure, weight losses averaged 7 8 percent for T. palustris and 31.6 percent for T. versicolor. Isocyanate-bonded control... 

The most reliable and convenient method to determine the total (end group and isocyanate) NCO is titration. A known amount of an amine (dibutylamine is used in the reference) is added to a weighed amount of prepolymer in solution. The amine reacts with the NCO groups and the excess amine, if titrated with a standard HCl solution, to a bromothymol blue end point. The amount of NCO is calculated as milUequivalents per gram of prepolymer or mass percent of NCO. Both measures are appropriate. 

Fig. VII-6. (a) The absorption coefficients of isocyanic acid in the vacuum ultraviolet. k is given in units or atm 1 cm"1 at room temperature, base e. From Okabe (765), reprinted by permission. Copyright 1970 by the American Institute of Physics. (b) Percent absorption of isocyanic acid in the near ultraviolet. Pressure is 100 torr and path length is 10 cm. From Dixon and Kirby (287), reprinted by permission of The Chemical Society.

The amount of isocyanate in a commercial isocyanate or isocyanate-containing formulation usually will be specified as weight percent isocyanate (as NCO) or as an amine... 

MDI is a solid at room temperature with a melting point of about 38°C, which usually is stored and shipped in the molten state for convenience. However, on standing in the liquid state, the MDI slowly dimerizes, and the liquid MDI becomes saturated with dimer at about 1 percent dimer by weight. The dimer then begins to precipitate. The isocyanate content of the remaining liquid will then remain constant. 

The optimum reaction conditions for reaction with epoxides are a 95/5 (v/v) mix of epoxide with triethylamine at 120°C and 150 psi nitrogen. Depending on the isocyanate used, reaction conditions of 120°C and 150 psi with no catalyst and 5 percent triethylamine or 5-35 percent dimethylformamide are optimum. 

Percent isocyanate = the percent by weight of isocyanate (NCO) groups present. The amine equivalent, AE, is the weight of sample which reacts with 1 gram-equivalent weight of dibutyl amine (reaction 1-13). 

In principle, both the one-shot process and semi-prepolymer processes have been used for rigid-urethane-foam manufacturing. However, the monomeric TDI-based one-shot process was used only in the initial stage of the rigid-urethane-foam industry because of the toxicity problems of TDI and difficulties in controlling reactivity due to the high NCO percent. For these reasons TDI-prepolymers, blends of TDI prepolymers and polymeric isocyanates, and 100% polymeric isocyanate are most widely used. 

In this paper, the hard segment content is defined as the percent by weight of the isocyanate and extender in the polymer at a fixed stochiometry or isocyanate index. 

Percent Yield bp °C/torr mp °C fto25 Isocyanate Equivalent Found Calc. 

Polyurethanes are the major products in which isocyanates are used. The percent of total polyuretahnes in different uses is given in Table III. 

The fact that these concentrations have been measured does not mean that occupational exposures occur persons may use respiratory protection equipped to prevent exposure. All persons who have excessive occupational exposure to isocyanates may experience primary irritant effects in the respiratory tract depending on the extent of excessive exposure. Brief accidental exposures to concentrations of isocyanates tenfold or more above the TLV may cause short term respiratory irritation with recovery 24-48 hours following cessation of exposure. Continuing repeated workday exposures several-fold higher than the TLV can cause chronic respiratory irritation. All individuals will not suffer the same degree of respiratory irritation from excessive exposures due to individual biochemical and physiological differences. Studies have shown that on the order of five percent of persons who have had an occupational exposure to TDI develop a bronchial asthmatic type of response to subsequent exposures that are below concentrations causing any detectable primary irritation. 

An example of a polyurethane adhesive used for surface mounting components consists of Mondur M cured with castor oil or with other polyols. The molecular weight and properties of polyurethanes are optimized when one equivalent weight of the isocyanate reacts with one equivalent weight of the polyol. The equivalent weights are based on the percent of hydroxide of the polyol and the percent of isocyanate of... 

Prepolymers are isocyanates and react like isocyanates, with several important differences. Prepolymers typically are much higher in molecular weight, are higher in viscosity, are lower in isocyanate content by weight percent, and have lower vapor pressures. Prepolymers are important to adhesives for a number of reasons. The desired polymeric structure of the adhesive can be built into the prepolymer, giving a more consistent... 

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